Food selection and ingestion depend critically upon the sensory modalities of the mouth. The long-term goal of this project is to understand how the somatosensory and gustatory systems work together to serve these vital functions. Results obtained during the current funding period have provided new information about the kinds of perceptual interactions that do and do not occur between these systems as well as the psychophysical factors that underlie them. Hypotheses generated from these results will be further developed and tested in 4 specific aims. Aim 1 will investigate the effect of "active" versus "passive" tasting on perception of taste, oral somesthesis, and their perceptual interactions. Normal tasting is an active process that occurs within the context of correlated mechanical stimulation, yet taste perception has been studied almost exclusively as a passive reception of chemical stimulation. Experiments will test hypotheses that the ability to perceive some taste stimuli (particularly glutamates), chemesthetic stimuli (chemicals that produce burning or stinging sensations) and tactile stimuli (viscosity, astringency) depends on the mode of tasting and where in the mouth stimulation occurs. Aim 2 will test the hypothesis, based on new findings, that individual differences in taste perception are independent of individual differences in somatosensory perception, and that taste sensitivity is better assessed by use of a prototype taste stimulus (e.g., sucrose) than by the widely used bitter tastant PROP, to which many individuals are aguesic. Aim 3 will provide further tests of a hypothesis, based on recent findings, that bitter taste and burning 'pain'have a close perceptual relationship that arises from their common function as sensory signals of potentially harmful stimuli. Finally, aim 4 will combine psychophysical measurements with fMRI to study the central neural processing of taste and chemesthesis. The proposed study includes tests of specific hypotheses about the relationship of bitter taste to chemesthesis and the presence of a central neural 'gain'that contributes to individual differences in taste but not somatosensation. By providing new data on the perceptual properties and neural basis of normal taste, oral somesthesis, and their interactions, the proposed studies have the potential to improve clinical assessment of gustatory and oral sensory pathologies (e.g., 'burning mouth syndrome') as well as to provide new insights into their possible causes.